1. Field
Example embodiments relate to a method for forming an organic layer pattern, an organic layer pattern, and an organic memory device comprising the pattern. Other example embodiments relate to a method for forming an organic layer pattern which is characterized by forming a thin layer by coating a coating solution including a polyimide-based polymer having a heteroaromatic pendant group including a heteroatom in its polyimide major chain, a photoinitiator and a crosslinking agent on a substrate and drying the substrate, and exposing and developing the thin layer, an organic layer pattern, and an organic memory device comprising the pattern.
2. Description of the Related Art
With the advancement of information and communication industry in recent years, the demand for various types of memory devices is increasing. Especially, memory devices for mobile terminals, smart cards, electronic cash, digital cameras, game machines and/or MP3 players may be non-volatile implying that the information written therein is not deleted although the power is turned off. Most of such non-volatile memories may be silicon-based flash memories.
The existing flash memories may be confronted by several limitations, e.g., the frequency of writing/erasing is restricted, the writing speed is relatively slow, the production cost of a memory chip is increased due to a refinement procedure for achieving increased integrated memory capacity, and it may be impossible to further miniaturize the memory chip because of technical limitations.
As such technical limitations on the existing flash memories have been revealed, extensive research on the development of a next generation non-volatile memory device with increased speed, increased capacity, decreased power dissipation and decreased price is actively underway to overcome the above-mentioned technical limitations.
There are, as the next generation memories, a ferroelectric RAM, a magnetic RAM, a phase change RAM, a nanotube memory, a holographic memory and/or an organic memory depending on the material of a cell that is a fundamental unit inside a semiconductor.
Among them, the organic memory may achieve the memory characteristics by introducing an organic substance between a primary electrode and a secondary electrode, applying voltage thereto and employing bistability of a resistance value corresponding to the voltage. The organic memory may be a memory made in a manner that the resistance of the organic substance between the primary and the secondary electrodes may be reversibly varied by an electrical signal to write and read data ‘0’ and ‘1’. Such organic memory has drawn attention as a next generation memory because it may improve processability, cost production and integration degree that are the disadvantages of existing flash memories while maintaining non-volatile characteristics.
FIG. 1 is a perspective view schematically illustrating one embodiment of a memory matrix using a conventional organic memory device. As illustrated in FIG. 1, the memory matrix may be fabricated on a proper substrate, e.g., glass and/or silicon. This memory matrix may include a primary electrode 10 and a secondary electrode 30, and an organic active layer 20 between. In such a structure, the cell formed at a cross point of the primary electrode 10 and the secondary electrode 30 may provide bistability characteristics. For the fabrication of such a memory cell array, there may be a need for patterning the organic active layer as well as the electrodes. As the organic memory device becomes miniaturized and highly integrated, patterning the organic active layer into a desired shape and size may become more important.
In a conventional method for patterning an organic active layer of an organic memory device, where the organic active layer is a single molecule, a shadow mask may be embodied by heat deposition or e-beam deposition, while where it is a polymer, the pattern may be formed by an etching step using a separate photoresist. For example, the latter method may be carried out by coating a conductive material on the whole surface of a glass substrate to form a lower electrode, coating a photoresist composition including an organic active layer material thereon, and selectively etching and patterning the organic active layer by using a photoresist mask. However, this photoresist method is disadvantageous because the process is complicated and the cost is increased by use of relatively expensive equipment.
As other methods for patterning an organic layer, there may be a soft lithography method and an ink jet method. In these methods, the soft lithography method may form a pattern by dissolving a watersoluble photosensitive resin composition in water, coating it on the surface of a glass substrate and drying the substrate, exposing the photoresist layer thus obtained through a shadow mask and developing the layer, forming a photocurable pattern on the glass substrate by removing an unexposed area, coating a photo-absorptive material on the whole surface thereof and drying the same, and peeling-removing the photocurable pattern and the photo-absorptive material thereon. However, because this soft lithography method employs a mechanism of curing an active layer with heat or light, there may be a limitation on the selection of raw materials.
Meanwhile, the ink jet method has several disadvantages because it cannot technically apply for the formation of a submicron pattern due to nozzle blockade and it may be difficult to select a suitable solvent and maintain a constant concentration.